Changes in gut-associated flora and bacterial digestive enzymes during the development stages of abalone (Haliotis diversicolor)

Abstract

The gut of abalone contains a diverse population of bacteria which contribute to food digestion and nutrient absorption. To investigate the development of gut microflora in the small abalone Haliotis diversicolor and the effect of various diets on the bacterial communities, we analyzed the composition of gut microbial flora and the bacterial digestive enzymes in connection with four important development stages, i.e., larva, early-juvenile, late-juvenile and grow-out. Among these cultivated bacteria, the Firmicutes group was isolated from both the larval and early-juvenile stages; the CFB (Cytophaga/Flexibacteria/Bacterioides) group was detected in early juveniles, late juveniles and grow-out; the γ-proteobacteria existed throughout the four development stages. The isolated Bacillus sp. and Pseudoalteromonas sp. dominated in the larvae and were rarely detected in other stages. Subsequently, the genus Vibrio predominated in the latter three phases after the first feeding. Cluster analysis of the DGGE (Denaturing Gradient Gel Electrophoresis) patterns was basically congruent with the result of culture-dependent method in which the gut bacterial community indicated the successional change in the development stages. And the artificial diets contribute to the change of gut bacterial composition to some extent. The enzyme assay showed that the gut bacteria isolated from the early juveniles produced the greatest diverse digestive enzymes compared with those isolated from other development stages. Most cultivated bacteria in each development stage showed protease, lipase or alginate-degrading activities which could help the farmed abalone H. diversicolor to digest diets. All results showed that a unique but interrelated bacterial flora was developed in the abalone gut which was coincident with the change of diets.